The thread queuing function allows you to control whether or not threads should be queued up while waiting for TCBs to become available. You can accomplish this by switching the synctype attribute of a thread between synchronous and asynchronous mode. With synchronous mode for example, if a process can only have 50 TCBs active at any one time, then only 50 threads can be created. The 51st thread create results in an error. With asynchronous mode, however, you can set the synctype attribute for a thread such that the 51st thread is created. This thread will not start until one of the other threads finishes and releases a TCB.